Ionizing radiation presents a direct hazard to people; therefore, the dose a person receives should be minimized. Dose is related to the energy absorbed by the person. Dose minimization is best done by avoiding all unnecessary radiation exposure and minimizing necessary radiation exposure. In any event, the degree of exposure can be controlled if a person monitors his exposure; therefore, a real time warning device, monitoring and alarming the person of radiation exposure, is desirable. The devices presently used for detecting and warning of radiation dangers are large and expensive. These features prevent every person at risk from using one on a continual basis.
Standard radiation monitoring methods, film and thermoluminescent detectors (TLD), only record accumulated dose. They do not provide a contemporaneous warning of current radiation exposure but their use is mandated by the government to record accumulated dose of radiation. If a person exceeds his yearly dose, he can no longer work in a radiation area and the person or company responsible is notified accordingly.
In an article entitled "A New Tiny Computerized Radiation Dosimeter," by M. A. Wolf et al., a wristwatch dosimeter is disclosed. No provision is made in the wristwatch to determine dose at different skin depths. Also, the wristwatch counts photons. This photon counter is different from the present inventive concept of collecting charged ions. The accuracy of measurement in the wristwatch is a function of the energy of the X-rays.
In an article by A. Arbel et al., entitled "Development of a Portable Microdosimeteric Radiation Protection Monitor Covering a Dynamic Range of 120 dB Above Noise," a dosimeter is described using tissue equivalent gas in an ion chamber. The advantage of tissue equivalent gas is that current measured by the device is accurate in units of rad, or radiation absorbed dose. The Arbel monitor does not utilize a volume of gas immediately atop an integrated circuit (IC) and a collector electrode on the surface of the IC in direct contact with the gas. Further, Arbel does not use the collector electrode incorporated within an amplifier in the IC. Also, Arbel uses the logarithm of an amplified signal from the ion chamber.
D. A. Waechter et al. describe in an article entitled "New Generation Low Power Radiation Survey Instruments," a standard portable dosimeter system. The portable monitor consists of a Geiger-Muller tube (GM tube) with an event counter which records the number of ionizing events. There is a readout display and an audio alarm. The problem with the GM tube is that its response is not linear with the energy of the radiation, so its accuracy varies with radiation energy, although it is useful for warning.